Who played Raj Koothrappali in 'The Big Bang Theory'?

Who played Leonard Hofstadter in 'The Big Bang Theory'? Who played Penny in 'The Big Bang Theory'? In which TV series is Penny a main character? Who played Howard Wolowitz in 'The Big Bang Theory'? Who played Blair Waldorf in 'Gossip Girl'? In which TV series is Blair Waldorf a main character? Who played Serena van der Woodsen in 'Gossip Girl'? Who played Michael Westen in 'Burn Notice'?